Final answer:
To avoid overheating while preparing to dive in a cool mountain lake on a hot summer day, put your dry suit on prior to preparing your equipment to avoid sweating and experiencing evaporative cooling.
Step-by-step explanation:
In order to avoid overheating while preparing to dive in a cool mountain lake on a hot summer day, you should put your dry suit on prior to preparing your equipment. By doing so, you will avoid sweating and experiencing evaporative cooling, which can lead to discomfort and potential health issues.